The proliferation of wireless communication devices in unlicensed spectrum and the ever increasing consumer demands for higher data bandwidths has placed a severe strain on those frequency spectrum bands. Examples of the unlicensed bands include the 915 MHz, the 2.4 GHz Industrial, Scientific and Medical (ISM) band, and the 5 GHz Unlicensed National Information Infrastructure (UNII) bands. New devices and new standards emerge continually, for example, the IEEE 802.11b, IEEE 802.11a, IEEE 802.15.3, HiperLAN/2 standards. The emergence and acceptance of the standards has placed, and continues to place, a further burden on those frequency bands. Coexistence among the many systems competing for radio-frequency (RF) spectrum is taking on an increasing level of importance as consumer devices proliferate.
Persons skilled in the art know that the available bandwidth of the license-free bands (and the RF spectrum available generally) constrains the available data bandwidth of wireless systems. Furthermore, data-rate throughput capability varies proportionally with available bandwidth, but only logarithmically with the available signal-to-noise ratio. Hence, to transmit increasingly higher data rates within a constrained bandwidth requires the use of complex communication systems with sophisticated signal modulation schemes.
The complex communication systems typically need significantly increased signal-to-noise ratios, thus making the higher data rate systems more fragile and more easily susceptible to interference from other users of the spectrum and from multipath interference. The increased susceptibility to interference aggravates the coexistence concerns noted above. Furthermore, regulatory limitations within given RF bands constrain the maximum available signal-to-noise ratio and therefore place a limit on the data-rate throughput of the communication system. A need therefore exists for a high data-rate communication apparatus and system that can readily coexist with other existing wireless communication systems, and yet can robustly support relatively high data-rates in a multipath environment.